Kenwood TW 4000a Has Keyup But No Transmit

[Raccoon]

So I recently purchased a Kenwood TW 4000a , and I realize it's a 30 year old radio ... that's one of the reasons I wanted it .
It receives good ... and it has keyup , but no transmit . When I key the mic , I can see the signal bar moving with my audio , but I don't hear any audio transmitting on the radio I'm listening with ... and it doesn't trip the local repeaters . And before anyone asks , yes the receiving radio is on the right frequency ... lol

I was wondering if anyone might have an idea as to why . Is it Electrolytic Capacitor related , or does it have something different going on ?

Thanks

 

[Rwb]

1st question,does it have tone board? memory battery good? if it has tone board is switches set correctly per required tone for that repeater?
mine needed a new memory battery and it acted crazy till i changed it.
you can get like 2 diffrent tones per settings seems like .i got mine set up for 4 local repeaters that are all 91.5 pl
great old radios,love the shade of green it has.
also run lights on dim or your goin to hobby lobby lots for new green lite bulbs

 

[Raccoon]

I was testing it out on Simplex to begin with . I'd key the Kenwood up and say my call sign , and I can see the keyup on the Kenwood's display . The audio bar moves with my voice ... but I'm not hearing any audio coming from any of the receiving radios I used (I tested it with a few different radios) . I then went to a few different local repeaters that don't require CTCSS tones ... and nothing . It wasn't tripping them at all . It's weird that I can see it move with my voice , but not hear anything coming from it . It receives , but no transmit . Being that it's as old as it is , the first thing I did was put a new battery for the memory in it ... and yes , it does have both the CTCSS tone board , and the VS-1 voice board installed in it .

 

[Rwb]

im not more help than what i mentioned.surely we got a member with an idea maybe handy andy

 

[BJ radionut]

http://www.radiomanual.info/schemi/KENW_VU/TW-4000A_user.pdf

I recall this radio having a strange MIC Hook-up. I believe there are several references even in the manual about using ONLY the supplied Kenwood microphone with this radio. I remember this having a non-standard wiring due to using with tone and voice board.
This rig does not use a Dynamic mic like most Kenwood's of that era. This one had a special electric (condenser mic) element and had special function buttons for tones/voice board operation. (?)
PAGE: 9 of manual
GL
All the Best
Gary

 

[Raccoon]

Actually this radio still has it's original stock mic with it

 

[Rwb]

are you using a diplexer? correct antenna connection to band? they have both uhf and vhf so239 on back.
vhf is to the left if your looking straight at the back,close to the power cord,uhf is on the far right.
use either 2 antennas or a diplexer connected to both so 239 then to antenna wire. after rethinking sounds like you might be hooked to uhf transmitting on vhf or visa versa. just my suggestion and observation at this point. if that dont help ive gone as far as i can helping you.let us know if that be the problem
oh yes some of the early tw 4000 had type N connectors check that out too. the 259 will screw on but messes the inner part up

 

[Dmans]

I can see the keyup on the Kenwood's display . The audio bar moves with my voice ... but I'm not hearing any audio coming from any of the receiving radios I used

I would put a frequency counter in line. From your statement above, it appears to be transmitting but on what frequency?

73
David

 

[Handy Andy]

im not more help than what i mentioned.surely we got a member with an idea maybe handy andy

I usually get jumped on...

But this is sounding like an Age related issue. Even a Keying circuit issue...

Especially when a used radio arrives and it won't transmit.

The unit works using low-level modulation - so part of the path that moves the "mod meter" works, can't tell much by that. But to know you do not have any emissions means you've lost part or all of the IF that mixes the Audio into it and produces the RF out in that TX stage.

I think this is your radio... If not ignore...

So, The PLL unit, uses two transistors to toggle I'm ok - let's go... moments

Q1 for 2M and Q6 for that 440 band...

IF you don't get any output on those transistors - suspect them or the PLL unit they're on - to need work.

It needs the Mic board (your audio) to give it an IF signal to determine the health of the main chassis of the radio

Note the novel use of MB3756 and the 2SC1815 - Kinda like those old Cobras...
14C and 43C comes off of this to "turn on" the rest of the radio for that band selected...

There is also another spot I find interesting and vulnerable - as in a potential Achillies heel...

See J3? An external jack in which to use those TX togglers' (ahemn) 14C and 43C (Connector 3 and output on Connector 4) from that AVR unit (main 144MHz board) tap here.

So, to me, I'd look to see if J3 and those TX transistors that run on the TX side - even work - try them on 144 and the 440 bands ...

Anyone Got a schematic?

Else if I got it right...you can thank...

Not responsible for omissions, obituaries, obfuscations, objections or anything else used in the post that others may find obscure - including the rest of the letters in the alphabet....

 

[Raccoon]

Thanks everyone ... and WOW Andy , you put in some time for researching it ... lol .

To answer the 1st question ... I am using a 2m/440 duplexer , hooked up correctly ... and it's hooked up to a 2 meter antenna . I put my FT-897D on the same frequency that the TW-4000a is on . They're both on Simplex . I can key the 897D and hear it coming through the TW-4000a ... but if I key the TW-4000a up ... I can see the key-up on the meter of the Kenwood ... but I'm not hearing any audio , or seeing a signal coming from the Yaesu .

David , I haven't checked out if it's transmitting on frequency or not ... but I'll look into that real quick and see .

and Andy .... if I have any of that going on with it , than it looks like it's going to have to take a trip to my radio doctor ... lol . It really has me confused since it's completely performing as it should ... but without transmit audio .

 

[Handy Andy]

Thats why I worry, could be something simple but as long as you can hear carrier it produces on another radio - that is most of the battle.

I just hope it's something like a dried-out cap

 

[Rwb]

Thanks everyone ... and WOW Andy , you put in some time for researching it ... lol .

To answer the 1st question ... I am using a 2m/440 duplexer , hooked up correctly ... and it's hooked up to a 2 meter antenna . I put my FT-897D on the same frequency that the TW-4000a is on . They're both on Simplex . I can key the 897D and hear it coming through the TW-4000a ... but if I key the TW-4000a up ... I can see the key-up on the meter of the Kenwood ... but I'm not hearing any audio , or seeing a signal coming from the Yaesu .

David , I haven't checked out if it's transmitting on frequency or not ... but I'll look into that real quick and see .

and Andy .... if I have any of that going on with it , than it looks like it's going to have to take a trip to my radio doctor ... lol . It really has me confused since it's completely performing as it should ... but without transmit audio .

like i said.hang in there we get somebody to sort this out

 

[Raccoon]

The electrolytic capacitors were my first thought . That's why in my first post I asked "Is it Electrolytic Capacitor related , or does it have something different going on ?" . With these older radios , the electrolytic capacitors are almost always the culprit when something goes wrong ... lol

 

[Raccoon]

My "Radio Doctor" thinks it might be the microphone ... I'm at such a loss right now ... I have no idea where to start anymore .